Control valve and positioner diagnostics

ABSTRACT

Valve positioning systems may include one or more components and a controller. Components may include one or more electric-to-pressure output converters, relays, gas supplies, and/or actuators. A controller may adjust a position of a valve by sending a signal. The valve positioning system may individually monitor components and determine the condition of each component being individually monitored. The valve positioning system may determine if a component will fail prior to failure and/or determine if a problem will occur in a component prior to the problem occurring.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/620,584, filed on Jan. 1, 2007, and claims the benefit thereof under35 U.S.C. §120.

TECHNICAL FIELD

This invention relates to valve positioning systems and methodsperformed by valve positioning systems, and more particularly toself-diagnosing valve positioning systems.

BACKGROUND

Control valves are used to regulate fluid flow in a wide variety ofcommercial and industrial systems. Today, many control valves includeand/or are controlled by automated positioners, which may have theability to adjust the valve to control fluid flow for a process. Somepositioners may even be able to self-calibrate. Down-time incurred torepair and/or replace control valves and/or positioners and/or loss ofproduct from the process due to the low quality produced while a controlvalve and/or positioner are malfunctioning may increase production costsand decrease efficiencies for the process.

While detection of a problem in a fluid control system may be identifiedwhen the quality of a process deteriorates, the source of the problem inthe system may not be identifiable in this manner. Fluid control systemsinclude numerous components that can have problems such as failure,leaking, breaking, and/or operating irregularly, such as limit cycles.Problems with systems are typically only detected once a problem occurs.However, once a problem occurs, a process may have already beenadversely affected by the problem. Furthermore, some systems may requirethe control valve to be brought off line for diagnosis, which caninterrupt the process. Other systems may allow on-line detection, butmay only detect problems after failure or when the system is operatingirregularly, which may still harm the process.

SUMMARY

A valve positioning system may include a number of components and acontroller. In one implementation, the components and the controller maybe positioned in a housing. At least one of the components of the valvepositioning system may include an electric-to-pressure output converter.Components may also include relays, gas supplies, and/or actuators.

A controller may individually monitor components of the valvepositioning system and determine the condition of components beingmonitored. Determining the condition of a component may includedetermining if the component will fail prior to the component failingand/or determining if there will be a problem with the component priorto the problem occurring.

A valve positioning system may include sensors coupled to the inlet andthe outlet of a component. A sensor may transmit a signal being measuredto the controller. The controller may compare signals from an inlet andan outlet of a component. In one implementation, a signal for the inletfor a component may be the signal for the outlet of another component.

In some implementations, the valve positioning system may individuallymonitor at least one component, such as an electric-to-pressure outputconverter and/or an actuator. The valve positioning system may determinethe condition of each component being monitored. The valve positioningsystem may determine if a component is failing or will fail at leastpartially based on the determination of the condition of a component.The system may determine if a problem will occur prior to the problemoccurring in a component at least partially based on the determinationof the condition of a component. In some implementations, the valvepositioning system may compare signals from the inlets and the outlet ofeach component being individually monitored and determine the conditionof a component based at least partially on the comparison.

In particular implementations, a valve positioning system may adjust aninput signal into at least one system component such that a valveactuator is inhibited from responding to the input signal change.Adjusting the input signal may include terminating the input signaland/or transmitting a high frequency signal. The valve positioningsystem may determine input and output signals at one or more of thecomponents. One or more sensors may determine input and/or outputsignals. The valve positioning system may determine a condition of acomponent based at least partially on the comparison of input and outputsignals of the component. In some implementations, the valve positioningsystem may determine if one of the components will fail prior to failureof the component and/or determine if there will be a problem with one ofthe components prior to the problem occurring at least partially basedon the determination of the condition of a component.

Various implementations may have one or more features. For example, onefeature of a valve positioning system may be the ability to monitorwhile the valve is operating. Allowing on-line monitoring may reduceoperating costs since downtime may be reduced and/or redundant valvepositioning systems may not be needed. Another feature may include thecapability to detect problems with a component prior to failure. Theability to detect problems prior to failure may reduce downtime and/ordecrease the effect of the failure on the valve positioning system(e.g., earlier detection of a problem in a component of the valvepositions system may result in less product being adversely affected byinaccurate positioning of a valve). A feature of the valve positioningsystem may include isolation of a problem with and/or failure of acomponent in the system, which may decrease downtime and/or allow moreefficient replacement and/or repair of components.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features,objects, and advantages will be apparent from the description anddrawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a flow chart illustrating one example of a process performedby a valve positioning system.

FIG. 2 is a block diagram illustrating an example of a fluid controlsystem.

FIG. 3 is a block diagram illustrating another example of a fluidcontrol system.

FIG. 4 is a flow chart illustrating a process performed by a valvepositioning system.

FIG. 5 illustrates a representation of an input/output curve for anelectric-to-pressure output converter.

FIG. 6 illustrates a representation of an input/output curve for arelay.

FIG. 7 illustrates a representation of an input/output curve for ameasured pneumatic train input signal and a relay output signal.

FIG. 8 illustrates a representation of an input/output curve for anelectric-to-pressure output converter.

FIG. 9 illustrates a representation of an input/output curve for arelay.

FIG. 10 illustrates a representation of an input/output curve for ameasured pneumatic train input signal and a relay output signal.

FIG. 11 illustrates a representation of an input/output curve for anelectric-to-pressure output converter.

FIG. 12 illustrates a representation of an input/output curve for arelay.

FIG. 13 illustrates a representation of an input/output curve for ameasured pneumatic train input signal and a relay output signal.

FIG. 14 illustrates a representation of a fluid control system.

FIG. 15 illustrates a representation of a portion of a fluid controlsystem.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

A valve positioning system may include a controller and various othercomponents. The controller may control a position of a valve and monitorcomponents of a valve and/or the valve positioning system. For example,the controller may adjust a position of a valve in response to an inputsignal (e.g., a signal from a remote process controller and/or anoperator). The controller may also analyze signals from the monitoredcomponents to determine a condition of a valve and/or a valvepositioning system and/or components of the valve positioning system.

Components of a valve positioning system may include converters,sensors, relays, gas supply lines, fluid supply lines, and/or actuators.Converters may convert a signal received from a controller. For example,an electric-to-pressure output converter (“E/P converter”) may convertan electrical signal from a controller to a signal that is a flow of afluid or gas, such as air, natural gas, or other appropriatecompressible gasses. Sensors may be any device capable of measuring asignal (e.g., electrical or pressure) produced and/or received by thevalve positioning system. For example, a sensor may measure parameterssuch as, but not limited to, pressure, flow rate, electrical current,electrical voltage, and/or a valve position. Relays may transmit and/oramplify signals received. Relays may include, but are not limited to, aspring-diaphragm actuator, a spool valve, or a pneumatic amplifier. Anactuator may respond to the signal from the converter. An actuator, mayfor example, include a piston subject to differential pressure.

A valve positioning system may be self-diagnosing. For example, thevalve positioning system may be capable of determining the condition ofvarious components of the system. Utilizing self-diagnosis in a valvepositioning system may allow quicker detection/identification ofcomponent failures in the valve positioning system and/or problems withcomponents prior to failures or problems arising. Problems may include,but are not limited to, mechanical problems and/or failures withportions of a component (e.g., valves, lines, connections, andregulators), problems and/or failures with electrical components of thecontroller, shift in electronics such as software problems or problemswith filters applied in the electronics.

FIG. 1 illustrates an example of a process 100 performed by a valvepositioning system. The valve positioning system may individuallymonitor components of the valve positioning system (operation 110). Forexample, monitoring the components of the valve positioning system mayinclude monitoring input and output signals for one or more components(e.g., current to pressure transducer and/or relay). In particularimplementations, input and output signals for each component may bemonitored. The valve positioning system may determine the condition ofeach component being monitored (operation 120). By determining thecondition of a component of a valve positioning system, problems orfailure of a component may be more accurately predicted. For example,problems or failure of a component may be isolated to a single component(e.g., gas supply) rather than attributed to the entire valvepositioning system. Furthermore, an error in a valve positioning systemmay be attributed to the appropriate component (e.g., a leak in a gassupply connection to an electric-to-pressure output converter ratherthan attributing the error to a component that is functioning properly(e.g., an electric-to-pressure output converter)).

In some implementations, components may be continuously and/orperiodically monitored, which may result in more accurate valveoperation and/or greater predictability of failure of components of thevalve positioning system. Components may be monitored at least onceevery 24 hours, in some implementations. Trending analysis, input/outputcurves, etc. may be performed to facilitate prediction of failure orproblems with components.

In some implementations, an input signal to one or more of thecomponents may be modified. For example, the input signal may beinterrupted, a high frequency signal may be sent, and/or the inputsignal may be modified for a time period too short for the mechanicalcomponents of the fluid control system and/or the valve to react. Theinput and output signals to one or more of the components of the fluidcontrol system may then be monitored and the condition of the monitoredcomponents may be determined. Modifying the input signal to a componentmay facilitate identification and/or isolation of a problem in the fluidcontrol system.

FIG. 2 illustrates one example of a fluid control system 200. Fluidcontrol system 200 includes a valve positioning system 300. Valvepositioning system 300 may include a controller 500 and at least twocomponents 600, 700. Sensors 900, 1000, 1100, 1200 may be coupled toinlets and/or outlets of components to determine signals transmittedand/or received by the components.

During use, an input signal 400 (e.g., a 4-20 mA signal) may be sent tocontroller 500. A sensor 900 may measure the signal received by thecontroller. Controller 500 may transmit a signal to first component 600(e.g., an electric-to-pressure output converter), which may be measuredby a sensor 1000. First component 600 may transmit a signal to secondcomponent 700 (e.g., a pneumatic relay or an actuator), which may bemeasured by a sensor 1100. Second component 700 may transmit a signal toa valve 800. The signal transmitted to valve 800 from second component700 may adjust the position of the valve. A sensor 1200 may measure thesignal transmitted to valve 800. In some implementations, sensor 1200 oranother sensor may determine a position of valve 800.

In some implementations, the controller and one or more of thecomponents may be positioned in a housing. The housing may at leastpartially enclose at least one of the components and the controller. Thehousing may be weather resistant, explosion resistant and/or proof,and/or meet government and/or industry standards. Positioning thecontroller and/or components in the housing may facilitate installationof the valve positioning system and/or prevent damage to componentsand/or controllers.

FIG. 3 illustrates another example of a fluid control system 1300. Thefluid control system includes a valve positioning system 1310, anactuator 1800, and a valve 1900. Valve positioning system 1310 may becoupled to a gas supply 1600 and/or actuator 1800. Valve positioningsystem 1310 includes a controller 1400 and an electric-to-pressureconverter 1500 and a relay 1700 (e.g., a spool valve or a pneumaticamplifier). In particular implementations, actuator 1800 may be acomponent of the valve positioning system 1310.

Controller 1400 may be coupled to an electric-to-pressure outputconverter 1500. Gas supply 1600 (e.g., air or natural gas) may becoupled to and deliver gas to the electric-to-pressure output converter1500 and/or relay 1700. Relay 1700 may transmit and/or amplify receivedfluid signals. In the illustrated implementation, valve positioningsystem 1310 includes a single relay 1700. In other implementations,however, the valve positioning system may include multiple relays. Forexample, a valve positioning system may include a relay above and belowa piston of an actuator (not shown). Relay 1700 may be coupled toactuator 1800. Actuator 1800 may be coupled to valve 1900 and adjust aposition of the valve.

Valve positioning system 1310 also includes sensors coupled to inletsand outlets of the components. The sensors may be positioned proximate acomponent being monitored. In some implementations, a sensor at an inletof one of the components may be analogous to a sensor at an outlet ofanother component (e.g., an input signal of one component may be thesame as an output signal of another component). A sensor 2000 maymonitor a input signal 1320 received by controller 1400. The sensor 2100may measure a temperature proximate controller 1400. Ambienttemperatures greater than a predetermined temperature may cause one ormore components to deteriorate. A sensor 2200 may monitor a signaltransmitted from controller 1400 to electric-to-pressure converter 1500.A sensor 2300 may monitor a signal transmitted from electric-to-pressureconverter 1500 to relay 1700. A sensor 2400 may be coupled to the gassupply to measure (e.g., flow rate, amount, or pressure) the gas streamtransmitted from the gas supply to electric-to-pressure output converter1500 and/or relay 1700. A sensor 2500 may measure a signal transmittedfrom relay 1700 to actuator 1800. A sensor 2600 may measure a positionof valve 1900.

The controller may receive signals representing measured parameters fromthe sensors. In some implementations, the signals may be stored. Thecontroller may include a processor and a memory. A processor may be anyprogrammable logic device, such as a microprocessor, a microcontroller,or a field programmable gate array (FPGA). A memory may include acomputer system memory such as DRAM, SRAM, EDO RAM, RDRAM, etc., or anon-volatile memory such as a magnetic media (e.g., a hard drive),optical storage, or EEPROM. The memory of the controller may store datasuch as signals from sensors and/or conditions of components.

The processor of the controller may include instructions to individuallymonitor components and determine a condition of each of the components.Received signals and/or inputs from operators may be stored in thememory of the controller. The controller may analyze the signalsreceived from components of the fluid control system and/or compare thesignals received to previous signals received and stored in the memoryof the controller. For example, trending analysis may be performed onthe received signals. In particular implementations, stored signals maybe used to determined input/output curves for analysis of a componentcondition.

In some implementations, the controller may transmit a message inresponse to monitoring the signals. For example, a message may betransmitted to an operator that identifies the condition of a componentof the valve (e.g., impending failure of a component).

FIG. 4 illustrates an example of a process 2700 performed by a valvepositioning system. Process 2700 may, for example, illustrate theoperation of valve positioning system 1510 in FIG. 3. Components of thevalve positioning system may be individually monitored based on theirinput and output signals (operation 2710). For example, a controller ofa valve positioning system may receive and analyze signals from sensorscoupled to components of the valve positioning system monitored duringnormal operations.

Individually monitoring components of the valve and/or valve positioningsystem during normal operations may allow problems in components of avalve to be detected prior to the problems occurring. Normal operationsmay include when the fluid control system is operating in steady state,stable, or when nothing appears to be wrong in the fluid control system,as opposed to a malfunctioning fluid control system (e.g., limitcycles).

Signals from the inlet and the outlet of each monitored component may becompared (operation 2720). The relationship between the inlet and theoutlet of a component may be known and/or predictable. Thus, signals atthe inlet and the outlet may be monitored, and the condition of thecomponent may be determined. For example, signals at an inlet and anoutlet of an electric-to-pressure converter and/or an actuator may bemonitored to determine the condition of each component. The signals frominput and outlet of a component may be compared using a variety oftests, such as, but not limited to, comparing input/output curves,f-test, Fourier transforms, or wavelet analysis. In someimplementations, a theoretical output signal is determined from themeasured input signal. The measured output signal may be compared to thetheoretical output signal.

In particular implementations, the signals from the inlet and the outletof each monitored component may be compared to data stored in a memoryof a controller and/or a remote memory. Comparison of the signals todata stored in a memory may be used to determine a condition of acomponent. For example, input and output signals for a component thatdeviate more than a predetermined amount from stored data that includeshistorical signals for input and output signals may indicate that thecomponent will fail and/or a problem will occur with the component.

The condition of each component being monitored may be determined basedat least partially on the comparison(s) (operation 2730). For example, aproblem such as a leak in an electric-to-pressure output converter maybe determined based on a comparison of input and output signals to theelectric-to-pressure output converter (e.g., a signal transmitted fromthe controller to the electric-to-pressure output converter, ameasurement of a gas stream transmitted from the gas supply to theelectric-to-pressure output converter, and the output signal from theelectric-to-pressure output converter). The valve positioning system maydetermine if one of the components being individually monitored isfailing based at least partially on the determination of the conditionof the component (operation 2740). For example, properties of acomponent prior to failure may be known and the valve position systemmay monitor components for these known properties. The valve positioningsystem may determine if a component will fail prior to failure and/ordetermine if a problem will occur in a component prior to the problemoccurring.

Using process 100 and/or 2700, for example, a valve positioning systemmay determine component conditions such as, but not limited to, pluggingof electric-to-pressure output converters, deposits onelectric-to-pressure output converter flexures or nozzles, failure ofcontroller electronics, performance shift of controller electronics,failure or leak in a relay (e.g., failure or leak in a diaphragm of arelay), gas leaks in tubing connections (e.g., to an actuator, a relay,or an electric-to-pressure output converter), broken actuator springs,increased packing friction, low pressure gas stream delivery from gassupply, and/or temperature outside a predetermined range (hightemperatures may cause failure in a few days). For example, if themeasured output signal is not within a predetermined range of thetheoretical output signal, the condition of the component may havedeteriorated. In some implementations, a valve positioning system maydetermine if a component is exhibiting behavior associated with failure.In other implementations, a valve positioning system may determine if acomponent of the valve is broken (e.g., a connection is leaking orloose, a converter is not making the appropriate conversion, an actuatoris sticking, etc.).

FIGS. 5-7 illustrate example input/outlet signal curves for a normallyoperating valve positioning system. FIG. 5 illustrates a representationof an input/output curve for an electric-to-pressure output converter.FIG. 6 illustrates a representation of an input/output curve for arelay. In another implementation, FIG. 7 illustrates a representation ofan input/output curve for a pneumatic train. The pneumatic train mayinclude an electric-to-pressure converter and a pneumatic relay. Thus,an input to the pneumatic train may be, for example, an input signal toan electric-to-pressure converter, and an output from the pneumatictrain may be, for example, a relay output signal. As illustrated in FIG.7, the pneumatic train appears to be operating normally.

FIGS. 8-10 illustrate example input/output signal curves for a valvepositioning system with a small air leakage in the line feeding theactuator. Since the input/output signal curve for theelectric-to-pressure output converter appears to be normal in FIG. 8,but the input/output signal curve for the relay in FIG. 9 includes anoutput that does not appear to be normal, the condition of thecomponents may be determined. In this illustration, the condition of theelectric-to-pressure output converter is normal, but there is a problemor will be a problem in the relay. FIG. 10 illustrates an input/outputsignal curve for a pneumatic train. The input of the pneumatic traininput signal (e.g., current to an electric-to-pressure converter) isgraphed versus a relay output signal, which is the output signal fromthe pneumatic train. As illustrated in FIG. 10, there is a problem orwill be a problem within the pneumatic train (e.g., electric-to-pressureconverter and pneumatic relay). The input/output curves of thecomponents of the pneumatic train (see, for example, FIGS. 8-9) may beanalyzed after a problem in the pneumatic train has been identified todetermine where the problem is occurring and/or what the cause might be.

FIGS. 11-13 illustrate example input/output signal curves for a valvepositioning system with a large air leakage. The input/output signalcurve for the electric-to-pressure output converter appears to be normalin FIG. 11. However, the input/output signal curves for the relay inFIG. 12 include an output that does not appear to be normal. Thus, thecondition of the components may be determined. The condition of theelectric-to-pressure output converter is normal in this illustration,but there is a problem or will be a problem in the relay. FIG. 13illustrates an input/output signal curve for a pneumatic train. Theinput/output curve is a graph of a measured pneumatic train input signal(e.g., current to an electric-to-pressure converter) versus a relayoutput pressure, which is the output of the pneumatic train. Asillustrated in FIG. 13, there is a problem or will be a problem withinthe pneumatic train. The input/output curves of the components of thepneumatic train (see, for example, FIGS. 11-12) may be analyzed after aproblem within the pneumatic train has been identified to determinewhere the problem is occurring and/or what the cause might be.

In some implementations, a determination of the condition of a componentmay be based on input/output signal curves, such as for an actuator orother component comprising a single inlet and a single outlet.Identification and/or isolation of a problem or a failure developing ina component of the valve positioning system may also be facilitated byuse of more than one input/output signal curve. For example,determination of a condition of a component may be based on more thanone input/output signal curve when a condition of a relay is beingdetermined since a relay may be coupled to a gas supply, anelectric-to-pressure output converter, and an actuator.

The systems and processes discussed above may have a variety offeatures. One feature of a valve positioning system and process may bethe ability to determine if a problem or failure will occur in acomponent of the system prior to the problem or failure occurring.Predicting problems and/or failures may decrease operating costs due tolost productivity when a component fails. Furthermore, identifyingand/or isolating a problem to a component of the valve positioningsystem may reduce down-time for repair and/or replacement of thecomponent.

Another feature of a valve positioning system and process may be on-linemonitoring. On-line monitoring may allow a valve positioning system tocontinue to operate during monitoring. On-line monitoring may reduceoperating costs by reducing the amount of redundancy needed in a system(e.g., extra valve positioning systems may not be necessary when asystem is capable of on-line monitoring).

In some implementations, a valve positioning system may be used insafety-instrumented systems (e.g., emergency shut-down valves and othersystems with high reliability standards). Use of valve positioningsystems capable of diagnosing problems and/or failures prior to theproblem or failure occurring may meet and facilitate compliance withregulations of safety-instrumented systems.

Particular implementations of valve positioning systems and processesmay use an input signal to one of the components to facilitatediagnostics. The input signal may be adjusted such that an actuator forthe valve is inhibited from responding (e.g., by adjusting the positionof the valve) to the input signal change. For example, an input signalto a component may be terminated or modified for a period of time smallenough such that an actuator is inhibited from responding. In someimplementations, the input signal may be terminated or modified for aperiod of less than 10 ms. Since the signal returns to the originalsignal after termination or modification of the signal for less than 10ms, the actuator and the valve may be inhibited from responding to theterminated and/or modified signal. As another example, a high frequencyinput signal may be transmitted such that the actuator is inhibited fromresponding (e.g., the mechanical components of the actuator may beunable to respond to a high frequency input signal). For example, a highfrequency input signal may be above the cutoff frequency for theactuator and below the cutoff frequency for components being monitored.In certain implementations, inhibiting the actuator from responding mayresult in the actuator not responding.

As a further example, the input signal may be adjusted (e.g., higher orlower) for a predetermined period of time (e.g., for 1 millisecond, 1microsecond, or any other appropriate period of time) after which theinput signal is allowed to return to its previous value. Thepredetermined period of time and/or adjustment may be small enough thata valve actuator is inhibited from responding. For example, forces suchas friction or fluid dampening may inhibit an actuator from respondingquickly. Thus, since a signal may be adjusted (higher/lower) for a briefperiod of time prior to returning to its previous valve, the valveactuator may not move or move insignificantly (e.g., movement of theactuator due to the adjustment of the input signal may not substantiallyaffect the fluid control).

The signals at an inlet and an outlet of component(s) due to theadjusted input signal may be monitored. The condition of a component maybe determined based on the comparison of the input signal and the outputsignal of the component.

Adjusting an input signal may allow components of the valve positioningsystem to react (e.g., cause signals transmitted from the component(s)to adjust) while not substantially altering the position of the valve.This may allow the condition of components of the positioning systemand/or valve to be determined without substantially affecting theposition of the valve, and, hence, a regulated process. In someimplementations, the input and output signals for one or more of thecomponents may be measured in response to the adjustment of the inputsignal. The condition of the component may be determined based on theinput and output signals for the component. For example, the input andoutput signals may be compared and the condition of the component may bebased at least partially on the comparison. In certain implementations,the input and output signals of most, if not all, of the components ofthe positioning system and/or valve may be measured and compared.

FIG. 14 illustrates an example fluid control system 3000. Fluidregulatory system 3000 may also include a controller 3001 and anoverride circuit 3002. Input signals (e.g., process setpoints, etc.) maybe transmitted directly to an input interface 3020 of controller 3001and/or to override circuit 3002. Controller drives theelectric-to-pressure (E/P) servo circuit 3026, which delivers a currentcommand signal to E/P converter 3003.

E/P servo controller 3026 may be any hardware and/or software forgenerating control signals to E/P converter 3003 in response to commandsreceived from controller 3001. The control signal sent from the E/Pservo controller 3026 may be adjusted based on data from sensors (e.g.,sensors 3010-3017). For example, the control signal sent from the E/Pservo circuit 3026 may be adjusted based on data received from apressure sensor 3016 coupled to actuator 3006. The control signals arecommunicated from the E/P servo circuit 3026 to the override circuit3002, allowing the override circuit 3002 to produce control signals forthe electric-to-pressure converter 3003.

Override circuit 3002 may provide safety control features to fluidcontrol system 3000. For example, if unsafe conditions exist in oraffect fluid control system 3000, override circuit 3002 may modify orinterrupt an input signal (e.g., process setpoint 3019, control signalto E/P converter 3003, etc.) provided to or by the fluid control systemto provide a signal that causes the fluid control system to go to a“safe state” (e.g., vent fluids to atmosphere, close valves, or anyaction appropriate for a specific system). As an example, if a processsuch as a chemical reaction becomes uncontrollable, the override circuit3002 may interrupt the signal from controller 3001 to the E/P converter3003 and cause the fluid control system 3000 to go to a safe state(e.g., closing a feed line to the process). As another example, if aleak of unsafe material is detected, the override circuit 3002 maymodify the signal to cause the fluid control system 3000 to close avalve 3007 upstream of the leak.

Input and output signals for the components of fluid control system 3000may be determined by sensors 3010-3017. A current sensor 3010, forexample, may be coupled to E/P servo circuit 3026 to determine a currentinput signal (e.g., from controller 3001). Current sensors 3011, 3012may be coupled to an inlet and outlet of override circuit 3002 todetermine the current input signal to the override circuit (e.g., fromE/P servo circuit 3026) and the current output signal from the overridecircuit 3002 (e.g., to the E/P 3003). Pressure sensors 3013, 3014, 3015,3016 may be coupled to the outlet of the E/P converter 3003, outlets ofthe pneumatic relay 3004, and/or air supply 3005. A sensor 3017 (e.g.,travel sensor) may determine the position of the valve 3007.

The data from sensors 3010-3017 are transmitted to input interface 3020of controller 3001. Additionally, discrete inputs 3018 (e.g., tripsignals and other types of signals) and the process setpoint 3019 (e.g.,position of valve desired during operation) may be transmitted to inputinterface 3020. The input interface 3020 may provide the informationfrom sensors 3010-3017 and other inputs to the firmware 3030 executed bya microprocessor 3025 of fluid control system 3000. Data from monitoringand/or results of analysis of the data may be stored in a nonvolatilememory 3034 of the microprocessor 3025.

Override circuit 3002 may be implemented using digital components,analog components, or a combination thereof. Override circuit 3002 maybe any collection of electronic components that can interrupt or modifythe communication of a signal to E/P converter 3003 without disruptingthe ability of the signal to power controller 3001 and/or sensors3010-3017. Override circuit 3002 may be located apart from controller3001, such as on a separate printed circuit board, or it may beintegrated with the controller.

In some implementations, input signal to override circuit 3002 may be atrip signal. A trip signal and/or a command signal may control operationof override circuit 3002. A trip signal may be regulated by an externalcontrol mechanism, which may base determinations on data received fromvarious parts of a regulation process and/or facility. Override circuit3002 may, for example, be triggered in response to receiving a tripsignal (e.g., for testing purposes or to cause a fluid regulatory systemto go to a safe state), detecting a change in the state (such as goingfrom high to low) of a command signal such as process setpoint 3019,detecting an interruption in the trip signal or the command signal,receiving notice of an unsafe condition, or any of numerous other eventswhich require operating fluid regulatory system in a safe state. Whenoverride circuit 3002 receives a trip signal, the modification performedon the control signal (e.g., from controller 3001 to E/P converter 3003)may be any suitable modification to cause the E/P converter 3003 toperform an action associated with the “safe state” (e.g., transitioningto a default state, such as closed, or freezing the current state). Forexample, some E/P converters 3003 vent to the atmosphere (e.g., a valveis opened that releases fluids in the fluid regulatory system to theatmosphere) when the control signal is interrupted.

Override circuit 3002, which may be viewed as a safety override circuitin one aspect, may have a variety of configurations. In certainimplementations, for example, override circuit 3002 may receive inputsignals before being provided to controller 3001. Thus, override circuit3002 may evaluate input signals and determine whether to modify theinput signal and/or control signal to E/P converter 3003 while stillallowing controller 3001 to extract power and communications from theinput signal. Modifying the input signal and/or control signal mayinclude boosting, attenuating, transforming, interrupting, converting,or otherwise manipulating the control signal to produce a particularresponse from E/P converter 3003. If the input signal does not indicatethat a condition is occurring, the control signal output by overridecircuit 3002 may be essentially the same as one that enters (e.g.,control signal from E/P servo circuit). In some implementations,override circuit 3002 may receive a trip signal in addition to orinstead of a command signal. Override circuit 3002 may also evaluate atrip signal to determine whether to modify the control signal to E/Pconverter 3003. If E/P converter 3003 vents to atmosphere during signalmodification, override circuit 3002 may restore the output pressure ofthe E/P converter to atmospheric pressure in response to an activationcondition.

To evaluate an input signal for modifying the E/P converter controlsignal, override circuit 3002 may, for example, include a transistorcoupled to the control signal line and controlled by a comparator. Thetransistor may be any suitable current- or voltage-controlled electroniccomponent that restricts or allows current flow in response to a signalat a control terminal (discussed here as a comparator). For example, thetransistor may be p-type or n-type field effect transistor (FET), suchas metal oxide semiconductor FET (MOSFET) that is controlled by avoltage applied to a gate terminal of the MOSFET. The comparator may beany circuitry for comparing a reference input signal to a thresholdinput signal (e.g., an op-amp) and producing an output to control thetransistor in response to the comparison.

In one implementation, override circuit 3002 may receive an inputcurrent generated from the command signal. A resistor may be coupled tothe negative line of the command signal and placed in parallel with adiode to develop a voltage proportional to the command signal's inputcurrent. A resistor may also be coupled to the positive line of thecommand signal to produce a characteristic voltage drop representativeof the command signal's input current. A voltage regulator may work withthe second resistor to form a constant reference voltage against whichthe voltage across the first resistor is compared.

In operation, the comparator performs the comparison of thecharacteristic voltage representative of the input current to thereference voltage. If the characteristic voltage falls out of range(e.g., below the reference voltage), because the input current is toolow or because the voltage regulator has shunted the input current toground because it was too high, the comparator turns off its respectivetransistor, thus interrupting current flow to the E/P converter. Inparticular implementations, the circuitry can be redundantly duplicatedto provide added security.

To evaluate a trip signal for modifying the control signal, overridecircuit 3002 may, for example, include a transistor in the positive pathof the control signal. The transistor may be any suitable current- orvoltage-controlled electronic component that restricts or allows currentflow in response to a signal at a control terminal (discussed here as avoltage regulator). The voltage signal used to control the transistor isthe trip signal, stepped down by the voltage regulator to a voltagelevel appropriate for the transistor. Thus, for example, a 24-V tripsignal could be stepped down for 5 V if the transistor was a 5-V MOSFET.The override circuit 3002 may also have a resistor coupled between thepositive path of the control signal and the gate line of the transistorto prevent current from the stepped-down trip signal from significantlyaltering the control signal. For example, the resistor may be selectedto have a relatively high resistance value, such as 1 MΩ, to minimizecurrent flow.

In operation, the transistor allows current flow as long as thestepped-down voltage from the trip signal is maintained. When the tripsignal is interrupted, the current flow through the transistor isinterrupted, thus interrupting the control signal to E/P converter 3003.In response to the interruption of the control signals, the E/Pconverter 3003 transitions to a safe state, such as venting to theatmosphere. Thus, the override circuit 3002 provides an effectiveoperation for stopping the control signal in response to the tripsignal. In particular implementations, the override circuit 3002 mayinclude two duplicate override circuits for increased reliability.

In certain implementations, the features of monitoring the commandsignal and monitoring the trip signal may be provided in one safetyoverride circuit override circuit 3002 (e.g., on the same circuitboard). In application, however, it may be that only one of the safetyfeatures is used. Furthermore, although mention has been made of theoverride device having redundancy through duplicate circuits, it may beadvantageous to provide redundancy through non-duplicate circuits, whichmay reduce the chance of both circuits being affected by the samecondition. In certain implementations, however, redundancy is notrequired.

Controller 3001 may include firmware 3030 to facilitate monitoringand/or diagnosis of problems in fluid control system 3000 and/orcomponents of the fluid control system. During operations, a valvepositioning algorithm with positioning diagnostics 3031 of firmware 3030may be utilized by controller 3001 to drive the E/P servo circuit 3026in response to input signals, monitor components of fluid regulatorysystem 3000, and/or diagnose the health of the fluid control systemand/or various components of the fluid control system. In someimplementations, controller 3001 may utilize other modules of firmware3030 to test the health of various components. For example, the signalto E/P 3003 may be modified (e.g., via E/P servo circuit 3026) using avalve positioning self diagnostic algorithm 3033 and/or valve diagnosticalgorithm 3034 to determine the health of components of the fluidcontrol system 3000. Although the firmware 3030 is described indifferent modules or portions 3031-3033, various portions of thefirmware may be combined. For example, the valve positioning algorithmwith positioning diagnostics 3031 may be a portion of or combined withvalve positioning system self-diagnostic algorithm 3033.

A switch 3050 (e.g., controller or servo signal, software switch, orfirmware switch) may allow the controller to drive the E/P servo circuit3026 using various modules of firmware 3030. Controller may utilize avalve positioning algorithm with positioning diagnostics 3031, valvediagnostic algorithm 3032, and/or valve positioning self-diagnosticalgorithm 3033. The data from monitoring components of the fluid controlsystem 3000 (e.g., in response to receiving process setpoint 3019) maybe analyzed using the valve positioning algorithm with positioningdiagnostics 3031 and valve diagnostic algorithm 3032. Valve positioningalgorithm with positioning diagnostics 3031 may diagnose the health ofcomponents of the fluid control system 3000. Valve diagnostic algorithm3032 may diagnose the health of components of the fluid control system3000. For example, the valve diagnostic algorithm 3032 may modify acontrol signal to the E/P servo circuit 3026 such that the valveposition is adjusted (e.g., by linearly modifying the signal), and thechange in valve position may be monitored. The health of the valveand/or actuator may be determined based on the modification to thecontrol signal. The controller 3001 may utilize switch 3050 to executevalve diagnostic algorithm 3032 and/or valve positioning systemself-diagnostic algorithm 3033 to test components of fluid controlsystem 3000.

FIG. 15 illustrates an example of a portion 4000 of the fluid controlsystem 3000 illustrated in FIG. 14. The switch 3050 allows controller3001 utilize various algorithms, as appropriate, to drive E/P servocircuit 3026, which delivers signals to control the E/P converter 3003.For example, during use, valve position may be determined according to aprocess setpoint. The valve positioning algorithm with positioningdiagnostics 3031 may individually monitor components (e.g., E/P servocircuit 3026, override circuit 3002, E/P converter 3003, relay 3004,and/or actuator 3006) while adjusting to a process setpoint specified.The valve positioning algorithm with positioning diagnostics 3031 mayanalyze data from monitoring components individually. For example, valvepositioning algorithm with positioning diagnostics 3031 may determine ifthe valve has difficulty adjusting to the process setpoint specified.The valve positioning algorithm with positioning diagnostics 3031 mayadjust the control signal delivered from the E/P servo circuit 3026 inresponse to the detected problem. For example, if the valve is havingdifficulty closing, the current signal delivered from E/P servo circuit3026 may be adjusted to adjust the pressure signal delivered from thecurrent-to-pressure converter to facilitate closing the valve.

Components of fluid control system 3000 may also be tested by modifyingan input signal delivered by the E/P servo circuit 3026. The valvepositioning system self-diagnostic algorithm 3033 may be capable ofperforming various modifications on the control signal delivered by E/Pservo circuit 3026 to components of the fluid control system (e.g.,override circuit or electric-to-pressure converter). For example, valvepositioning system self-diagnostic algorithm 3033 may modify a commandsignal and/or interject a signal into the command signal such as linearmodification 4051, a pulse signal 4052, and/or a sine signal 4053. Thetype of modification selected to test components may be based on thecomponent on which testing is performed. A linear modification of thesignal 4051 may, for example, be used to test the actuator 3006 and/orthe valve 3007 health. A signal may be linearly modified and theposition of the valve may be adjusted while monitoring the health of thevalve, actuator, and/or other components of the fluid control system. Asanother example, an actuator 3006 may include a spring in compressionwhen the valve is closed. The pressure signal delivered to the actuator3006 may be linearly increased to increase pressure delivered to aspring of an actuator of the spring (e.g., above the pressure requiredto cause the spring to close the valve) without changing the position ofthe valve and the health of components of the valve positioning system(e.g., E/P converter and/or relay) may be determined. Thus, in a fullyclosed valve, an input signal to components, such as the E/P converterand/or relay, may be modified and the pressure delivered to the actuatormay be increased as a result; however, since the pressure required toclose the valve is already being delivered to the spring, the positionof the valve may not be substantially affected (e.g., a mechanical stopmay inhibit the spring from further compressing as more pressure isapplied to the spring). Although the above example is described in termsof an air-to-close valve, a similar procedure may be used in air-to-openvalves (e.g., when a valve is fully opened, pressure delivered to thevalve may be increased without substantially affecting the position ofthe valve)

As a further example, the signal delivered to the E/P converter 3003 maybe linearly saturated and then desaturated to determine the health ofthe E/P converter and/or override circuit 3002. In addition, theoverride circuit 3002 may be tested using a pulse signal 4052. Since theshort time period of the pulse signal 4052 may inhibit mechanicalcomponents of the fluid control system from reacting to the pulsesignal, the override circuit 3002 may be tested while inhibiting achange in the valve 3007 position. Thus, the responsiveness of theoverride circuit 3002 may be tested without substantially affectingnormal operations. As another example, a command signal from E/P servocircuit may be modified to include a sine signal 4053 to test electricalcomponents of the fluid control system 3000 (e.g., override circuit 3002and/or E/P converter 3003) while inhibiting movement of the valve 3007position. As another example, the valve position may be temporarilymodified to determine a valve health and/or the health of othercomponents of the fluid control system 3000.

The output interface 3040 may receive the results of the analysis of thedata by valve positioning algorithm with positioning diagnostics 3031 orother modules of the firmware 3030 and send a signal to discrete outputs3041. Discrete outputs 3041 may include outputs that display the healthof one or more of the components of the fluid control system 3000 and/orthe overall health of the fluid control system. For example, a red LED3042 may indicate if a problem that requires immediate attention (e.g.,from an operator) exists with fluid control system 3000. A yellow LED3043 may indicate if a problem may exist with fluid control system 3000(e.g., valve 3007 is sticking or air is leaking from the air supply3005). A green LED 3044 may indicate if a fluid control system 3000 isin general good health (e.g., few or no problems in the fluid controlsystem).

In some implementations, asset management device 3070 may includesoftware that facilitates monitoring fluid control system health. Assetmanagement device 3070 may include a computer (e.g., in control room, ona personal digital assistant, on a smart phone, etc.) coupled to (e.g.,via one or more network protocols or directly) the fluid control system3000. A communication interface 3060 of the microprocessor 3025 ofcontroller 3001 may transmit data from monitoring components of thefluid control system 3000 to the asset management software for analysis.Asset management software may analyze the data using any of the testspreviously described or any other test to facilitate determining if aproblem exists with a component of the fluid control system 3000. As anexample, asset management software 3000 may determine the health ofindividual fluid control system components periodically.

The asset management device may include a graphical user interface thatfacilitates identification of problems and/or the health of componentsof the fluid control system. For example, the graphical user interfacemay include a representative schematic of the fluid control system andan indicator that indicates the health of the component. As anotherexample, a graphical user interface of asset management device may allowa user, such as an operator, to view tests and/or results of tests onindividual components of the fluid control system.

Several implementations for achieving fluid control system diagnosticshave been described, and a number of others have been mentioned orsuggested. Furthermore, those skilled in the art will readily recognizethat a variety of modifications, substitutions, deletions, and/oradditions may be made to these implementations while still achievingfluid control system diagnostics. The scope of the protected subjectmatter therefore is to be determined on the basis of the followingclaims, which may encompass one or more aspects of one or more of theimplementations.

It is to be understood the implementations are not limited to particularsystems or processes described which may, of course, vary. It is also tobe understood that the terminology used herein is for the purpose ofdescribing particular implementations only, and is not intended to belimiting. As used in this specification, the singular forms “a”, “an”and “the” include plural referents unless the content clearly indicatesotherwise. Thus, for example, reference to “a relay” includes acombination of two or more relays and reference to “a gas” includesmixtures of different types of gases.

1. A valve positioning system comprising: at least two or morecomponents, wherein at least one of the components comprises anelectric-to-pressure output converter; and a controller configured to:adjust a position of a valve by sending a command signal to theelectric-to-pressure output converter; individually monitor at least twoof the components of the valve positioning system by determining aninput signal to and an output signal from each of the at least twomonitored components; and determine a condition for each of the at leasttwo components being individually monitored at least partially bycomparing the respective input and output signals from each of the atleast two monitored components.
 2. The system of claim 1, furthercomprising an actuator, and wherein the controller is further configuredto individually monitor the actuator and determine the condition of theactuator.
 3. The system of claim 1, wherein the controller is furtherconfigured to determine a condition of a third component based on themonitoring of the at least two components, where the third component isnot a monitored component.
 4. The system of claim 1, wherein thecontroller is configured to determine if a particular one of the atleast two monitored components will fail prior to the particularcomponent failing or is failing when determining a condition of theparticular component being individually monitored.
 5. The system ofclaim 1, wherein the controller is configured to determine if there willbe a problem with a particular one of the at least two monitoredcomponents prior to the problem occurring when determining a conditionof a component being individually monitored.
 6. The system of claim 1,further comprising a housing at least partially enclosing at least twoof the components and the controller.
 7. The system of claim 1, furthercomprising sensors coupled to an inlet associated with the input signaland an outlet associated with the output signal of at least one of thecomponents being individually monitored, wherein the sensors areconfigured to transmit the input and the output signals of the componentto the controller.
 8. The system of claim 1, wherein at least one of thecomponents comprises a relay.
 9. The system of claim 1, wherein an inputsignal for at least one of the components comprises an output signal ofanother component.
 10. The system of claim 1, wherein the controller isfurther configured to: adjust an input signal to at least one componentof the valve positioning system such that a valve actuator is inhibitedfrom responding to the input signal change; wherein individuallymonitoring at least two of the components comprises determining inputand output signals for each of the at least one of the monitoredcomponents based on the adjusted input signal; and wherein a conditionof one of the components being individually monitored is determined atleast partially based on a comparison of the input signal and the outputsignal of the monitored component.
 11. A method performed by a valvepositioning system, the method comprising: individually monitoring atleast two components of a valve positioning system, wherein one of thecomponents comprises an electric-to-pressure output converter, bydetermining an input signal to and an output signal from each of the atleast two monitored components; and determining a condition for each ofat least two components being individually monitored at least partiallyby comparing the respective input and output signals from each of the atleast two monitored components.
 12. The method of claim 11, whereindetermining a condition of a third component is based on the individualmonitoring of the at least two components, where the third component isnot a monitored component.
 13. The method of claim 11, furthercomprising determining if a particular one of the at least two monitoredcomponents will fail prior to the particular component failing or isfailing at least partially based on the determination of the conditionof the particular component.
 14. The method of claim 11, furthercomprising determining if a problem will occur prior to the problemoccurring in a particular one of the at least two monitored componentsat least partially based on the determination of the condition of theparticular component.
 15. The method of claim 11, further comprising:adjusting an input signal to at least one component of the valvepositioning system such that a valve actuator is inhibited fromresponding to the input signal change; wherein individually monitoringeach of the at least two of the components comprises determining inputand output signals for at least one of the components based on theadjusted input signal; and wherein a condition of a particular one ofthe at least two components being individually monitored is determinedat least partially based on a comparison of the input signal and theoutput signal of the particular component.
 16. A method performed by avalve positioning system comprising: adjusting an input signal to atleast one component of a valve positioning system such that a valveactuator is inhibited from responding to the input signal change; anddetermining a condition of at least one of the components at leastpartially based on the adjusted input signal.
 17. The method of claim16, wherein adjusting the input signal comprises terminating the inputsignal.
 18. The method of claim 16, wherein adjusting the input signalcomprises transmitting a high frequency signal.
 19. The method of claim18, wherein transmitting a high frequency signal comprises transmittinga signal that is above the cutoff frequency of the actuator and belowthe cutoff frequency of the positioner components.
 20. The method ofclaim 16, further comprising determining if one of the components willfail prior to failure or is failing at least partially based on thedetermination of the condition of the component.
 21. The method of claim16, further comprising determining if a problem will occur prior to theproblem occurring in one of the components at least partially based onthe determination of the condition of the component.
 22. The method ofclaim 16, wherein determining a condition of at least one of thecomponents at least partially based on the adjusted input signalcomprises: determining input and output signals for at least one of thecomponents based on the adjusted input signal; and determining acondition of at least one of the components at least partially based ona comparison of the determined input signal and the determined outputsignal of the component.